Process of making zinc-white.



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PERQCESS' OF. MAKING ZINC-WHITE.

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d nflation of LettersPatent. Patented Sept. 1, 191 1, Application filed September 15, 1913. Serial No. 789,842.

T0 (ZZZ whom it mag/concern Be it known that I, Enr'sna B. Curran, a citizen of the United States, residing at Erie, county-of Erie, "and State ofPe'nnsylvania, have invented a certain new and useful Process of Making Zinc-White, of which the following is a specification.

My invention relates to processes of obtaining zinc white directly from ores and especially to processes of obtaining it from ores in the wet way.

The ores to which it is intended to applymy process are those in which the zinc occurs as a sulfid or carbonate, more generally the former. 4 a

In carrying out my process on sulfid ores I proceed as follows: The ore is'first crushed to the proper degree of fineness and roasted with free access of air in any desired roaster until the contained metals are fully oxidized. The sulfurous oxid (89,) formed during the roasting may be withdrawn from the roaster and converted into sulfuric acidin any well known way. The ore containing zinc and other metals in the form of oxids is then withdrawn from the roaster and allowed to become cold. After the ore has become cold, I treat itwith dilute cold sulfuric acid. The acid for this may be that obtained from the roasting of the sulfid ore. The sulfuric acid employed should be just sulficient in quantity to satisfy the zinc contained in the ore, as may be determined by analysis, and should be applied in a very dilute and cold state. These conditions are of importance since I havefound that if the acid be applied cold and dilute, the sulfate formed will be almost solely that of zinc, whereas it hot acid be employed sulfates of oth or contained metal will be formed which will appear as impurities in the product. If it is found that the temperature of the mixture rises materially on the addition of the acid it. should be applied more gradually, this rise in ten'iperature being due to the heat of formation of the zinc sulfate. The mixture-is then allowed to stand until all of the heat produced by the reaction shall have passed off. During this period itis found that it any sulfates other than zinc have formed due to a rise in temperature and it the sulfuric acid be properly proportioned, such sulfates are decomposed probably by a reaction of some remaining zinc oxid. After the mixture has become cool. the solution is separated from the solid matter in any usual or desired way, and the solution will be found to be a solution of zinc sulfate substantially free from other bodies. If a greater freedom from impurities, such as traces of iron, etc, is desired, it may be ob tained by crystallization and resolution in the *vell known manner, or in any manner known to those skilled in the art. Having now obtained a solution of substantially pure zinc sulfate it remains to obtain therefrom zinc White and this I do by adding to the above solution ammonia as a gas or liquid or ammonium hydrate, the effect of this addition being the precipitation of'the zincas a hydrated oxid. The precipitate being separated from the solution in any well known way, as for instance by means of a filter press, may be dried and ground and placed on the market for use as such as a pigment or in any of the well known mixtures. The solution containing ammonium sulfate may be treated by well l'rnown methods for the recovery of ammonia therefrom and one of the advantages of the use of ammonia or ammonium hydrate as the precipitant is the easy and economical recovery of the ammonia for reuse.

As above stated the process may be employed on ores containing carbonates and without change except that the preliminary roasting is omitted. It will also be obvious that hydrochloric acid may besubstituted for the sulfuric acid, and if the conditions above prescribed are followed, it will be found satisfactory, but the former acid will generally be preferred.

Ammonium carbonate may be employed as the precipitant if Zinc carbonate is desired as the product, but the zinc hydrate is more desirable as it is a better carrier of oil.

In the claims I have specified the use of a compound of ammonium, but it will be understood that I contemplate the use of ammonium or ammonia in other equivalent forms suitable for the purpose specified.

As heretofore stated, the ore on which my process is practised contains zinc and other metals in the form of oxids. These other metals are usually copper, iron and lead to which zinc is electropositive. All of these metals are converted into oXids by the roasting step and these oxids are treated gradually with a suitable water soluble acid, such as sulfuric acid, and a low temperature is maintain ed during such treatment. By such treatment the acid ions are caused to attack mainly the zinc oxids and the treatment is continued until enough acid has been added 7 to just about use up the zinc. Thejiuid conthe dissolved zinc salt is then taken away and is treated with asuitable precipiagenttoobtain the-zinc as an o'xid'or hydrate or both in the form of zinc white.

I claim: I

I 1. The herein described process of obtaining pigment which consists in treating a compound, containing a mixture of oxids ineludin zinc oxid, slowly with a dilute solu- "tion. oi; a suitable water-soluble acid, maintainingthe. temperature low during such treatment, whereby the acid ions attack ma nly the zinc oxid, continuing the treat-' 7 untilenough acid has been added to Just vabout use up the zinc, taking away the compounds with n, suitable water soluble acid, maintaining.thetemperature low during'such treatment, whereby the acid ions attuck" mainly the zinc oxid, continuingthe treatment until enough acid has been added -to justabout use up the zinc, taking away the fluid containing the dissolved zinc salt,

3. The herein described process of obtaining pigment, which consists in converting zinc and any associated metals to which zinc iselectro-positive in ziukiferous compounds, into oxids, crushing, treating slowly said compounds with a suitable water soluble acid, maintaining the temperature low during such treatment, whereby the acid ions attack mainly the zinc oxid, continuing the treatment until enough acid has been added to just about use up the zinc, taking'away the fluid containing the dissolved zinc 'salt, maintaining the fluid at a low temperature and in a state of quiescence, and precipitating the zinc therefrom as oxid by treating said solution With ammonia, substantially as described.

In testimony whereof I have hereunto subscribed my name.

ELISHrl B. current Witnesses: LLOYD B. WIoH'r,

A N. MITCHELL. 

